Locked up in the bowels of the medical faculty building here and accessible to only a handful of scientists lies a man-made flu virus that could change world history if it were ever set free.

The virus is an H5N1 avian influenza strain that has been genetically altered and is now easily transmissible between ferrets, the animals that most closely mimic the human response to flu. Scientists believe it's likely that the pathogen, if it emerged in nature or were released, would trigger an influenza pandemic, quite possibly with many millions of deaths.

In a 17th floor office in the same building, virologist Ron Fouchier of Erasmus Medical Center calmly explains why his team created what he says is "probably one of the most dangerous viruses you can make"—and why he wants to publish a paper describing how they did it. Fouchier is also bracing for a media storm. After he talked to Science Insider yesterday, he had an appointment with an institutional press officer to chart a communication strategy.

Fouchier's paper is one of two studies that have triggered an intense debate about the limits of scientific freedom and that could portend changes in the way U.S. researchers handle so-called dual-use research: studies that have a potential public health benefit but could also be useful for nefarious purposes like biowarfare or bioterrorism.

The other study—also on H5N1, and with comparable results—was done by a team led by virologist Yoshihiro Kawaoka at the University of Wisconsin, Madison, and the University of Tokyo, several scientists told ScienceInsider. (Kawaoka did not respond to interview requests.) Both studies have been submitted for publication, and both are currently under review by the U.S. National Science Advisory Board for Biosecurity (NSABB), which on a few previous occasions has been asked by scientists or journals to review papers that caused worries.

NSABB chair Paul Keim, a microbial geneticist, says he cannot discuss specific studies but confirms that the board has "worked very hard and very intensely for several weeks on studies about H5N1 transmissibility in mammals." The group plans to issue a public statement soon, says Keim, and is likely to issue additional recommendations about this type of research. "We'll have a lot to say," he says.